The mental health needs of veterans within the VA Healthcare system are notable. With the substantial increase over the past 10 years in veterans seeking Posttraumatic Stress Disorder (PTSD) treatment services, the VA system is straining to accommodate these needs, relying heavily on group-based treatments. The proposed research will take the next step in the literature on group psychotherapy for PTSD by examining a group cognitive behavioral treatment (GCBT) program with promising pilot data. This application supports a randomized controlled trial, which will compare GCBT with Supportive Group Psychotherapy (SGP). The trial will involve 196 male veterans with combat-related PTSD who will be randomly assigned to GCBT (n= 98) or SGP (n =98) to determine efficacy within a naturalistic care environment. Outcome data will be collected pre-treatment, mid-treatment, post-treatment, and 6- and 12- month follow-up. Two aims are included, one focusing on outcome with respect to PTSD symptom severity, the second focusing on treatment generalization to comorbid emotional disorders (major depressive disorder, generalized anxiety disorder, and alcohol abuse), and distress and impairment. Data will be examined using latent growth curve modeling, with emphasis on determining efficacy and effectiveness. The information provided by the proposed project could assist in developing more effective care models for individuals with chronic PTSD from numerous traumatic experiences. Additionally, this project represents an effort to move the literature on group-based treatments for PTSD ahead, through inclusion of advanced methodological and analytic approaches.